1. Field of the Invention
This invention relates to a pressure sensor which is widely used in pressure switches, pressure detectors, pressure measuring instruments, etc.
2. Description of the Prior Art
Hitherto, various types of pressure sensors have been used. One conventional pressure switch incorporating therein an exemplary pressure sensor will first be described, which is configured as shown in FIG. 3.
In this drawings, reference symbol a designates a housing, b a pressure receiving section provided in the housing a, and c a fluid path. Symbol d designates a diaphragm made of stainless steel or rubber which is shaped in the form of a thin plate for easy deformation. Symbol e designates an O-ring, f a cylinder, and g a piston. A piston rod h of the piston g is connected with a switch i provided inside the housing a. Symbol j designates a spring, and k a quide. As will be apparent from the drawing, the guide k is screwed in the housing a via thread grooves l. Thus, as this guide k is turned, the degree of elastic deformation of the spring j is regulated, so that the working pressure of the pressure switch can be adjusted.
To the pressure receiving section b is connected a pressure unit not shown, hence, a pressurized fluid is introduced from this pressure unit into the path c. When the pressure of the fluid exceeds the force exerted by the spring j, the diaphragm d deflects and the piston rod h moves in the direction of the arrow Ah in opposition to the spring j, so that the switch i is pushed and switched over. Thus, the foregoing assembly functions as the pressure switch.
However, the aforementioned pressure switch has the following drawbacks. That is, since the spring j is always urging the piston g in the direction of the arrow Aj, the spring j suffers fatigues and its resiliency changes as the result of secular change. Hence, the working pressure or setting value of the pressure switch varies. Therefore, adjustment of such a value must frequently be performed during the service.